Mixed packet photographic emulsions



Dec. 20, 1960 v. TULAGIN ETAL 2,965,484

MIXED PACKET PHoToGRAPHIc EMuLsIoNs Filed March 26, 1956 Maf fa/fa@ 165mm@ rama/Af 056?? /2 Marsa/1f WWA/70,95

United States Patent 2,965,484 MIXED PACKET PHOTOGRAPHIC EMULSIONS Vsevolod Tulagin and Robert D. Jackson, Binghamton, N.Y., assignors to General Aniline & Film Corporation, New York, N Y., a corporation of Delaware Filed Mar. 26, 1956, Ser. No. 573,799 7 Claims. (Cl. 96-55) The present invention pertains to hydrophobic silver halide grains, said grains dispersed in a highly non-water miscible liquid, water-sensitive or hydrophilic colloidal carriers containing such dispersions, and light sensitive emulsons containing a matrix of a water-sensitive or hydrophilic collofdal medium having dispersed therethrough immobile packets of a highly non-water miscible solvent surrounding hydrophobic silver halide grains with associated sensltizers and, if desired, color formers capable of yielding a dye image complementary in color to the light rays for which such hydrophobic silver halide grains are respectively sensitized, and methods for producing said grains and compositions.

Many years of effort have gone into the immobilization of sensitizers, color formers and silver halide grains in photographic carriers, such as ge'atin, polyvinyl alcohol and the like. The purposes behind the immobilization or non-migration of color formers and/ or sensitizers, per se, are rather obvious at this stage of the photographic art and need be touched upon but lightly.

It is usual in the manufacture of light sensitive color materials to employ in the photographic emulsions thereof color formers reactive with another agent, such as an 'oxidized primary aromatic amino developer, to form dye images. It is equally the practice to locate the color formers leading to the colored images in different layers of the color material. Were such coupler to wander from layer to layer, color degradation and distortion would inevitably ensue. This problem has been solved by making the color formers substantive to the colloidal carrier, by including in the color former a long aliphatic chain, or by associating the color former with a nonmigratory high molecular weight relatively high boiling oil, such as tricresyl phosphate or the like.

The migraton of sensitizer from layer to layer of color film has not been a particular problem. However, a real problem arises if this phenomenon is permitted to ensue in so-called variable contrast paper. In such materials, two photographic emulsions of quite different contrast, each senstized to different regions of the spectrum, are intermixed. The contrast of the image of such papers is controlled by the color of the exposing light. It is imperative in such materials to avoid migration of the sensitizers from grain to grain and also so-called contagious development wherein one exposed grain will cause several unexposed grains to become developable. In other words, it is essential that each emulsion function completely independently of the others present.

A number of suggestions leading to the solution of this problem have been made. These involve the employment of a specific sensitizer structure, the addition of the silver halide to dye sensitized emulsions followed by mixing the so-prepared emulsion with the other (U.S.P. 2,411,096) and the use of perhalogenated salts, such as sodium perchlorate (U.S.P 2,239,699).

For numerous years, color 'm has been prepared and vended in the form of integral monopaeks. The manufacture of such products is intricate and time consuming involving. as it does, the laying down of a number of light sensitive balanced coatings, one upon the other.`

Furthermore, sensitivity or speed is a factor to be struggled with, due to the distance apart of the various sensitized layers. As a result, the art has been continuously shooting for the optimum, to wit, a color film with only one sensitized layer containing the sensi- 1) Ease of preparation, i.e., decrease in the number of coating steps;

(2) Greater control in the manufacturing process;

(3) Superior quality in light sensitivity and resolution due to the cose proximity of the sensitized grains; and

(4) Simplification in processing.

It is no wonder, therefore, that time and money havev been poured into the creation or realization of a product. permitting the attainment of these desiderata.

A full gamut of photographic procedures has been run in eorts to devise a commercial "mixed grain film. These have ranged from the use of hardened, differently sensitized emulsion granules, first suggested by Wendt in 1937 (U.S.P. 2,168,182) and later in U.S.P. 2,618,553 to the formation of individual packets of silver halide grains, sensitizer and, if desired, color former. Most of the work has been in the latter category, all of which has been bottomed on endeavors to immobilize the silver halide grains in the emulsion so that they are alienated from their associates and, hence, capable of functioning as individualists rather than as part of the herd.

One of the early moves in this direction was keyed to the addition of modifiers of high molecular weight hav.ng the ability to dissolve the color former imbibed to the silver halide grain, whereby color former association with the modier would prevent its diffusion from the colloidal carrier. To this end, it was proposed to employ such high molecular weight compounds as polyvinyl alcohol, polyvinyl phthalate, gum arabic and the like (U.S.P. 2,289,803).

Subsequently, it was decided to produce hydrophobic emulsions (water repellent) and, in U.S.P. 2,304,939, it

was suggested that the colloidal carrier for the light sensitive salts be collodion rather than gelatin. This theory was elaborated on in U.S.P. 2,284,877 which suggested that the silver hallde be precipitated with color former and/or sensitizer in the presence of a Water insoluble',

resin, such as amber, shellac, and the like, .and a solvent therefor. The mixture thus obtained would then be dispersed in a water permeable colloid, such as gelatin. Itwas recognized, however, that the speed of this materialwould be quite low and the further suggestion was made that gelatin should be present at the time of precipitation or formation of the silver halides.

It was later proposed to use zein as the peptizing agent (colloid) in the formation of mixed grain packets. In this procedure, the silver halide is formed in zein to produce oil soluble packets which are then dissolved in benzyl alcohol. The resulting solution, to which sensitizers and/or color formers may be added, is then dispersed in a water receptive carrier, such as gelatin (U.S.P. 2,563,791). This procedure was claimed to be improved upon by the use of 'y-phenyl propyl alcohol in lieu of benzyl alcohol as the solvent (U.S.P. 2,490,749).

The next phase witnessed the formation of packets by use of a water soluble colloid, capable of being rendered Patented Dec. 20, 1960 Water insoluble, and the dispersion of the resulting packets in a water permeable colloid, such as gelatin or polyvinyl alcohol. ln this method, the silver haLde grains are dispersed in a colloid, such as alginic-acid, oxidized cellulose or the like, sensitizers and color" formers added and the whole made water insoluble by treatment with an alkaline earth metal salt, such as calcium c-h-lorlde, calcium acetate and similar compounds. rThe insolubilized product is then dispersed in a water permeable colloid to form individual sensitive grains immoblzcd in the aqueous phase (U-.S.P. 2,548,526).

A f-urther advance in the packet 'concept was claimed in British Patent 711,488 and U-.S.'P. v2,698,795 and U-.S.P. 42,698,796, which turned upon the use, for iev# veloping the silver halide grains with associated sensitizeifs and color formers, if desired, of a copolymer of styrene and -maleic anhydride, on the one hand, and a water soluble polymer 'containing salt `forming acid groups, on thel other hand, such as a 'copolymer of methacrylic acid and methyl-a-methacrylate. The colloidal carrier in this system is gelatin in which th'e silver halide is precipitated.

Another modification of the fpacket system appears in British Patent 718,494, in which separate silver halide emulsions are formed, hardened and thein dispersed in a water insoluble cellulose ether 'and a partially water miscible solvent, such as acetone o'r the like.

Attempts have also been made to rem-ove the gelatin from normal photographic gelatin emulsions and to disperse the isolated silver halide in colloidal carriers, such as polyvinyl alcohol or carboxymethyl cellulose. How ever, it has not been possible to isolate vthe silver halide grains from a gelatin emulsion and to disperse them in an oily or a water insoluble medium, for the reaon that the silver halides of normal photographic emulsions are hydrophilic. By hydrophilic is meant that the sliver halides are preferentially wetted by water and even though obtained in a dry state, if dispersed in a water insoluble medium, would leave such medium and go into water or an aqueous solution if shaken therew th.

Despite the great volume of work devoted to the packet system for mixed grain emulsions, the fact remains that, as yet, there is no known commercially available light sensitive material which invokes these principles. Thus, in British Patent 711,488 it is stated:

Pri-or .processes employing mixed packet emulsions have not been successful either because it was impots ble to secure colour separation with them, that is, effectively to prevent colour formation around unexposed silver halide grains, or because the coloured particles formed in the process were too grainy.

The vpattern Yfollowed by prior operators to effect and maintain the isolation of silver halidel grains in packets is-`self-evident from the above rsum. As previously noted, the silver halide in normal photographic emulsions has an inherent propensity to segregate in the emulsion. In the packet system generally Ifollowed, the idea has been, not to divest the silver halide grains of this natural propensity, but rather to imprison or entrap the grains through a hit or miss manner in a ce`l or enve'ope of 'a body foreign to the carrier matrix, such as a water insoluble or water soluble natural or synthetic resfn.

We have now discovered that we can isolate silver halide grains in a water permeable matrix by rendering such grains hydrophobic so that their tendency to segregate or coalesce is eliminated. Once the grains have been made hydrophobic, they are amenable "to dspers'on in an oily non-water miscible liquid and, if desired, wth sensitizers, color formers land other photographic emulsion adjuncts to form a packet readily 'dspersib'e in a wated permeable colloid, Surprisingly, each packet remins @fixed or isolated in its assigned sphere lin rthe matrix and is capableof functioning as an individual entity.

The isolation of silver halide grains by rendering the grains hydrophobic, dispersons of such grains in a highly, non-water miscible solvent, water-sens.tive or hydrophilic colloidal carriers containing such dispersi-ons, and light sensitive emulsions containing said drspersions along w-ith associated sensitizers and, if desired, color formers, constitute the purposes and objects of our invention, Y v

4Our invention is predicated upon the realization that silver halide grainsl in normal photographic emulsions are surroundedby Ian envelope 'of adsorbed gelatin which cannot be removed without dlsrupting the crystal and destroying the photographic properties thereof. We have ascertained, and these constitute the critical factors of our procedure, that such gelatin envelope is amenable to chemical treatment with a compound containing a hydrophobic radical and a group reactive with amino 'compounds to produce hydrophobic silver halide grains disperslble in an oily, non-Water miscible liquid. Dlspersions of such hydrophobic grains when emulsiiied in ygelatin solutions or the like are completely vimmobile therein, a fact readily demonstrated by microscopcexamination. For example, if silver halide grains surrounded by a gelatin hull are dispersed in phenyl ethyl alcohol and the resulting dispension is then emulsiiied in gelatin, the microscope reveals that the silver halide grains leave the solvent and wander into -the gelatin matrix. A 'simlla'r examination of a dispersion produced as above, with our hydrophobic system, establishes that the grains refuse to leave the solvent for 'the gelatin.

The preparation of highly sensitive emulsions containing the hydrophobic silver halide grains begins with a normal silver halide gelatin emulsion. Such emuson is subjected to Aenzymatic hydrolysis to destroy the excess gelatin and, to this end, there may be employed any number of enzymes, such as polydase, trypsin and the like. The enzymatic action is permitted to continue until the silver halide can be readily decanted. n shown by Dr. Frank Hamm, I. Applied Phys. 24, 1495- 1513 (December 1953), that such enzymatic digestion does not disrupt the gelatin envelope which surrounds each silver halide grain. It has been established by us that such enzymatic digestion does not alter the photographic properties of such grain. v

After the excess .gelatin has been destroyed, the silver halide .grains are separated from the aqueous mediuml by decantation, filtration or centrifugation.- The isolated solid is re-'suspendedin a normally liquid (i.e., liquid at room temperature) inertY non-aqueous organic solvent, such as acetone, mcthylethyl ketone, benzene, ethyl acetate or the like, and thoroughly washed ktoremove any residual free water. The solid in such solvent is then subjected to the action of a chemical reagent capable of rendering the surface of the gelatin envelope hydrophobic.

In its broadest sense the latter treatment consists in closely associating the gelatin envelope of each silver halide grain with a hydrophobic moiety (see Schwartz- Ferry, Surface Active Agents, Interscience Publishers, Inc., New York, 1949, pages l7-20),'preferably, a long aliphatic chain, i.e., containing ten or more carbon atoms. To this end, there may be employed compounds containing a hydrophobic radical, on the one hand, and a group readily reactive with amines, on the other hand, such as long chain acid anhydrides, acid chlorides, sul fonyl chlorides, isocyanates or chlorocarbonates. Such long chain aliphatic compounds are those normally ernployed in modifying surface `properties. such compounds are tetradecyl isocyana-te, hexadecyl isocyanate, myristyl isocyanate, myristic anhydride, palmityl anhydride, Vrnyr-istoyl chloride, -palmitoyl lchloride, stearoyl chloride, -myristylsulfonyl chloride, palmityh si'ilfon-yl chloride, stearylsulfonyl chloride, decylchloro- It has been Examples of carbonate, hexadecylchlorocarbonate, tetradecylchlorocarbonate, and the like. The treatment with these reagents is effected in normally liquid, inert organic solvents, such as, acetone, benzene, ethyl acetate, butyl acetate, methylethyl ketone and the like.

It is our theory that the reagents in question react with the gelatin hull to form either a covalent or coordinate bondage therewith. This theory is predicated on a number of factors, to wit:

(1) The activity of the anhydride, -acid chloride, sulfonyl chloride, isocyanate or chlorocarbonate groups insofar as amino groups are concerned and their ability to react therewith to form amides;

(2) The proposal in U.S.P. 2,179,244 to react gelatin with, inter alia, long chain acid chlorides;

(3) The fact indicated above that the silver halide, after treatment, is hydrophobic in the true sense of that term; and

(4) The silver halide grains are not rendered hydrophobic in the event that the reagent employed is relatively inert to amines, i.e., a carboxylic acid, per se, such as myristic acid.

In any case, if our theory of chemical conversion be incorrect, We are certain that a close physical or chemical association takes place between the involved reactants and the gelatin hull, which association leads to the formation of the hydrophobic silver halide grains. Typically, we have treated silver halide grains subjected to er1- zymatic digestion with myristic acid under the same conditions as such grains were treated with myristic anhydride. The grains so treated, when dispersed in phenyl ethyl alcohol and emulsified in gelatin, refused to remain in the solvent and migrated to the gelatin. It is thus evident that the association necessary to effect the desired hydrophobic condition cannot be obtained without using a compound having a grouping with a very marked tendency to react with amino groups to form amides.

After the treatment to impart hydrophobic character to the silver halide grains, the excess of the hydrophobating reagent is removed by washing with an organic solvent, such as acetone, and gradually replaced with another organic solvent which is to -be the final carrier for the transformed silver halide and which is an oily, non-water miscible liquid, such as benzyl alcohol, phenyl ethyl alcohol, 'y-phenylpropyl alcohol or the like, phthalic acid esters, i.e., dibutyl phthalate, di--ethoxyethyl phthalate, tricresyl phosphate, triphenyl phosphate, or a combination of such solvents.

The silver halide grain in such solvent is now added to non-aqueous solutions of color formers, sensitizing dyes, stabilizers and other adjuncts usual in the manufacture of photographic emulsions. The color formers employed are of the type capable of forming azomethine, quinoneimine or azine dyes on color development, i.e., they contain a phenolic hydroxy or reactive methylene group, are oil soluble and preferably contain an aliphatic chain of at least carbon atoms. Illustrative of color formers in this category are those described in Schneider et al., U.S.P. 2,186,849, without, however, a water solubilizing group being present in the color former molecule. The non-aqueous packets thus obtained are then dispersed in an aqueous solution of a water permeable colloid, such as gelatin, gum arabic, starch, polyvinyl alcohol, or carboxymethyl cellulose, with or without the aid of dispersing agents, as the occasion may demand and the operator may see tit to use. There are thus obtained stabilized, highly light sensi-tive dispersions, wherein the individual packets have no tendency to coalesce and function completely as individual entities. Preferably, the Water soluble carrier should be capable of gelation so that once cast or gelled, a rigid matrix is obtained.

The applicability of this system to the formation of mixed grain photographic materials is self-evident. Thus,

thislprocedure would permit theseparate sensitization of hydrophobic grains to the blue, green and red region of the spectrum along with color formers capable of giving a dye complementary in color to that of the spectral region to which the grains are sensitized.

The different packets may then be dispersed in one and the same water permeable colloid and the resulting emulsion coated and dried. Inasmuch as the various packets function as individual entities, a single exposure and color development with a primary aromatic amino developer such as the Ndialkyl-p-phenylenediamines, i.e., N-diethyl-p-phenylenediamine, 3-methyl-4-diethylaminoaniline, N--hydroxyethyl-N-ethyl-p-phenylenediamine and the like would produce images in the various` primary colors with adequate color separation being a.s` sured.

Our system lends itself readily to the formation of variable contrast emulsions. Here again, the immobility of the differently sensitized particles permits two different sets of silver halide grains in one and the same layer to function independently of each other.

Our emulsions, being non-aqueous, are less subject to degeneration on storage in areas of high humidity. This is an important aspect, particularly with regard to such high speed photographic film as X-ray and the like, and our system, therefore, recommends itself in the production of these materials.

Aside from its many different fields of application, our procedure has other important advantages. One of these is the ease with which dispersions of the non-aqueous emulsions can be made in aqueous media. Such dispersions are obtained by relatively mild stirring and energetic devices, such as colloid mills or other high energy mills, are unnecessary. Since only low energy dispersing machines are required, the dispersion can be accomplished without adversely affecting the photographic properties of the silver halides.

A further advantage resides in the fact that a drastic discontinuity between the packet and the matrix helps to isolate each individual packet and make it independent of chemical processes which may be taking place in an adjacent packet. Furthermore, it is possible to prepare packets of uniform size distribution and of almost any specified size. i

The invention is further illustrated by the accompanying self-explanatory drawing, Figure I of which indicates the distribution of silver halides in an emulsion according to our invention, and Figure II of which discloses the distribution of silver halides in an emulsion, prepared in the same manner as that of Figure I, but in which the treatment to impart hydrophobic character to the silver halide grains is eliminated.

The following examples will serve to amplify the specific procedure contemplated, but it is to be understood that the invention is not restricted thereto.

DIGESTION PROCEDURE Example I 50% acetone(by volume) followed by two washings` with acetone, using 150 ml. of solvent each time.

The Washes were removed by decantation. The silver halide may then be made hydrophobic as :subsequently described. i

Example II To 1000 grams of a melted added 100 ml. of 1% gelatin silver halide were trypsin as in Example I. After removall of` the digested gelatin, the precipitated silver halide was washed' with two 2,00 rnl. portions of 50% ethanol' followed by two washings with 95% alcohol, using 150-ml. each time. The product was then made hydrophobic as subsequently described.

HYDROPHOBIZING STAGE Example lll The silver halide isolated by enzymatic` digestion as in Examplel was suspended in a solution of 2.5 grams of myristic anhydride dissolved in 100 ml. of acetone.

Themixture was tumbled inlasmall roller mill for several hours and then allowed to stand until the silver halide Vhad settled. The acetone solution was decanted and the precipitate washed with two 150 ml. portions of fresh acetone. The damp. cake. was suspended in 30 rnl. of phenyl ethyl alcoholand stirred vigorously for 3 minutes in a small Waring blender. The resulting milky oil containing the hydrophobic silver halide is ready to be incorporated in packet or mixed grain photographic emulsions.

Example IV The silver halide obtained according to Example I was stirred up with a solution of 5.0 grams of myristic isocyanate in 100 ml. of acetone for l0 hours. The suspension was allowed to settle and the precipitate washedl twice with 200 ml. portions of acetone. The damp c-ake of hydrophobic silver halide was then dispersed in tricresyl phosphate to be used in the preparation of mixed grain photographic emulsions.

Example V Example Vl 'Ihe procedure was the same as in Example III, exceptingr that the.y hydrophobic character was imparted to the silver halideerains by treatment. with octadooyl chlorocarbonate.

Example VII The, procedure was the same as in Example V, excepting that tetradecylsulfonyl chloride was employed to render the silver halide grains hydrophobic.

PREPARATION OF MIXED GRAIN DISPERSIONS Example VIII 0.60 gram of 25% phenyl ethyl alcohol silver halide suspension prepared according to Example III was added to 30 ml. of 10%` gelatin andthe resulting mixture stirred vigorously for minutes. A dispersion was obtained consisting of minute oily droplets, 2 to 4 microns in diameter containing embedded hydrophobic silver halide crystals..

Exemple.l IX

0.0683 gram of l-pheuyl-3(l0-undecenoylamino)5 pyrazolone and .007 mg. of a green sensitizing dye were dissolved in a mixture oi`- 2.0 grams of tricresyl phosphate plus 2.0 grams of phenyl ethyl alcohol by warming on the steam bath. Next was added 0.274 gram of a 24% hydrophobic silver chloride-benzyl alcohol suspension prepared according to Example V and the whole thoroughly mixed and stirred up in 30 ml. of 10% gelatin until particles, ranging between 5 to 1 0 microns were..

obtained Example 0.0902 gram ofV yellow coupler (NhacetylAbenzoyiaootamidoshlfahilaoilide) was dissolved is. a mixtuo. of; 2.0 grams of; trioiosyl phosphate. alos 2-O, gratos of.. benzyl alcohol to which was added 0.274 gram of 24%. hydrophobic Silver Chlorido` Suspended ihy phenyl ethyl alcohol and the whole rhixod thoroughly- T-.his mixture.. was. thon dispersed. ih 30 IhlV o f 1.0% gelatin until particles measuring 5 to 10 micro/ns? were obta-inegl.4

Example X1 To 0.0764 gram of l-hydroxy-N-myrilstyl naphtharnidel and .007 mg. of a red sensitizing dye dissolved in a mixture ot 1.0 gram of phenyl ethyl alcohol plus 1.0 gram of the product sold by Atlas Powder Company as Span was added with good stirring 0.274 gram of 24% hydrophobic silver chloride suspended in( phenyl ethyl alcohol. This mixture was then dispersed in 30 rnl. of 10% gelatin by stirringl until the sizeY of the droplets were 5 to 10 microns. Y

Example XII To 0.0882 gram of l-phenyl-3-stearoylamino-S-pyrazolone and .01 mg. of a green sensitizing dye dissolved in a mixture of 5.71 grams of phenyl ethyl alcohol,

0.67 gram of tricresyl phosphate and 0.08 gram ofv N-butyl phthalate was added 0.545 gram of 20.9% hydrophobie silver chloride suspended in phenyl ethyl alcohol. This mixture was thoroughly stirred and then dispersed in 30 ml. of 10% gelatin until particles measuring 5 to 10 microns in diameter had resulted. Y

Example XIII To 0.152 gram of yellow coupler (4f-benzoylacetamido- N4caproylsulfanilanilide) dissolved in a Amixture of 5.71 ml. of phenyl ethyl alcohol and 0.63 ml. of tricresyl phosphate was added 0.397 gram of 34.5% hydrophobic silver chloride phenyl ethyl alcohol suspension and the whole thoroughly stirred. This mixture was dispersed in 30 ml. of a 10% solution of gelatin in a small Waring blender. Agitation was continued until a particle size of 5 to l0 microns was achieved.

MIXED GRAN DISPERSIONS Example XIV One part of the emulsion from Exemple IX was added to one` part of the emulsion from Example XI, and the resulting mixture gently stirred for 5. minutes. This mixed emulsion was coated on suitable lm base, dried and exposed through a step wedge and developed ina developing solution of the following composition to form a negative colored image:

N--hydroxyethyl-N-ethylfp-phenylenediamino farms-f. 5.0 Sodium sulte v g l do r 5 .0 Sodium carbonate .SHZO do 120.0 Po-t`ssium bromide .H do 1.0 Ethylene diaminetetraacetic acid do T 0.8 -Phenylethyl amine do 1.0

Water to make 1000.0 cc.

Separate cyan and magenta images were obtained.

Example XV One part of the green sensitive emulsion prepared in Example XII was added to one part of the blue sensitive emulsion from Example Xlil. The mixture was gently agitated for 3 minutes and then coated on suitable ilm base and exposed through a blue and green filter. Develcpment was carried out as described in Example XIV. Satisfactory color separation of magenta and yellow images. Wis. obtained in the Portions. of` theooaiihe exposed. to green and blue light, respectively. v

9 Example XVI Example X VII One part of the emulsion from Example IX, one part of the emulsion from Example X and one part of the emulsion from Example XI were added together and the resulting mixture gently stirred for a period of minutes. The mixed emulsion was coated on a film base, dried,

and exposed through a step wedge and developed in a i solution ofthe following composition:

3-methyl-4-diethylamino aniline grams 5.0 Sodium `sullite do 5.0 Sodium carbonate .3l-I2C do 120.0 Potassium bromide do 1.0 Ethylene diaminetetraacetic acid do 0.8 -Phenylethyl amine do 1.0

Water to make 1000.0 cc.

Separate negativesof yellow, cyan and magenta images were thus obtained.

Example XVIII The procedure is the same as in Example XIV, excepting that the color developing agent is N-diethyl-p-phenylenediamine.

Our invention, while particularly adapted for mixed grain emulsion work, may also be used to produce multilayer photographic color lm of the conventional type. Thus, a base may be coated sequentially with a red sensitized emulsion (Example XI), a green sensitized emulsion (Example IX) and a blue sensitive emulsion (Example X). This monopack iilm layer may be exposed and processed with the usual primary aromatic amino color developers to the three complementary colored images.

We claim:

1. A light-sensitive photographic emulsion comprising a hydrophilic colloid carrier having dispersed therethrough immobile packets of an oily, non-water miscible solvent surrounding light-sensitive silver halide grains which have been rendered hydrophobic by treating a light-sensitive gelatin silver halide photographic emulsion with a proteolytic enzyme in order to digest the gelatin carrier and produce silver halide grains each surrounded `by a hull of adsorbed gelatin, separating the light-sensitive grains and their adsorbed gelatin hulls from the digested gelatin and treating by intimately associating the gelatin hulls and said grains with an aliphatic compound having a hydrocarbon cha-in of at least 10 carbon atoms and a` substituent selected from the group consisting of acid anhydrides, acid chlorides, sulfonyl chlorides, isocyanates and chlorocarbonates.

2. The process of rendering silver halide grains hydrophobic which comprises treating a light-sensitive gelatin silver halide photographic emulsion with a proteolytic enzyme in order to digest the gelatin carrier and produce silver halide grains each surrounded by a hull of adsorbed gelatin, separating the light-sensitive grains and their adsorbed gelatin hulls from the digested gelatin and treating by intimately associating the gelatin hulls and said grains with an aliphatic compound having a hydrocarbon chain of at least 10 carbon atoms and a substituent selected from the group consisting of acid anhydrides, acid chlorides, sulfonyl chlorides, isocyanates and chlorocarbonates.

3. The emulsion as defined in claim 1, wherein certain of said silver halide grains are sensitized to one region of the spectrum and certain others are sensitized to a dilerent region of the spectrum.

4. The emulsion as defined in claim 1, wherein certain of said silver halide grains are sensitized to the red region of the spectrum and have lan oil soluble cyan color former associated therewith, others are sensitized for the green region of the spectrum and have an oil soluble magenta color former associated therewith, and others are sensitized to the blue region of the spectrum and have an oil soluble yellow color former associated therewith each of said color formers being capable of coupling with the oxidation product of an aromatic primary amino developing agent to form a dye.

5. The emulsion as deiined in claim 1, wherein the colloidal carrier is water permeable.

6. The emulsion as defined in claim 4, wherein the color formers contain an aliphatic chain of at least 10 carbon atoms.

7. The process of producing subtractive multicolor dye images in a single layer of a photographic emulsion, which comprises exposing a single layer of the emulsion of claim 4 coated on a base and developing the same in an N-dialkyl-p-phenylenediamine developer.

References Cited in the ile of this patent UNITED STATES PATENTS Y Hart et al Oct. 24, 1950 OTHER REFERENCES Hamm: Journal of Applied Physics, vol. 24, pp. 1495-1513, December 1953. 

1. A LIGHT-SENSITIVE PHOTOGRAPHIC EMULSION COMPRISING A HYDROPHILIC COLLOID CARRIER HAVING DISPERSED THERETHROUGH IMMOBILE PACKETS OF AN OILY, NON-WATER MISCIBLE SOLVENT SURROUNDING LIGHT-SENSITIVE SILVER HALIDE GRAINS WHICH HAVE BEEN RENDERED HYDROPHOBIC BY TREATING A LIGHT-SENSITIVE GELATIN SILVER HALIDE PHOTOGRAPHIC EMULSION WITH A PROTEOLYTIC ENZYME IN ORDER TO DIGEST THE GELATIN CARRIER AND PRODUCE SILVER HALIDE GRAINS EACH SURROUNDED BY A HULL OF ADSORBED GELATIN, SEPARATING THE LIGHT-SENSITIVE GRAINS AND THEIR ABSORBED GELATIN HULLS FROM THE DIGESTED GELATIN AND TREATING BY INTIMATELY ASSOCIATING THE GELATIN HULLS AND SAID GRAINS WITH AN ALIPHATIC COMPOUND HAVING AS HYDROCARBON CHAIN OF AT LEAST 10 CARBON ATOMS AND A SUBSTITUENT SELECTED FROM THE GROUP CONSISTING OF ACID ANHYDRIDES, ACID CHLORIDES, SULFONYL CHLORIDES, ISOCYANATES AND CHLOROCARBONATES. 